1. Field of Invention
This invention relates generally to thermotherapy, and more particularly to a universal applicator for domestic, professional or field use adapted to apply therapeutic heat to a localized skin surface of a patient whose threshold of sensitivity is determined by that temperature level of the heating medium to which the patient is exposed, above which the patient experiences discomfort or injury, the applicator subjecting the patient to periodic heat energy pulses having a peak temperature well above the temperature sensitivity of the patient, heat transfer taking place internally in the patient in the intervals between these pulses to an extent preventing an excessive rise in the temperature at the skin surface.
2. Status of Prior Art
The term "problem region" as used herein refers to a tumor, a set of muscles, or any other site underlying the skin which is causing difficulty and which lends itself to thermotherapy treatment.
The interior of the human body has a normal temperature level which is usually said to be 98.6.degree. F. But actually, in the course of each 24-hour period, the body temperature rises above or falls somewhat below this nominal value. Body temperature is determined by the relationship existing between the amount of heat internally generated, which depends on basal metabolism and the amount of heat escaping from the body. Additional heat is produced as a result of muscular activity, this being dissipated by an increase in radiation, conduction or evaporation from the skin surface and by more rapid and deep breathing.
Medical practitioners since ancient times have known that the application of heat to the body is useful in the relief of muscle soreness and various aches and pains, as well as in the treatment of certain pathological conditions. Thus the use of heat for the treatment of arthritis and other abnormalities is now commonplace. Hot water bottles and electrical heating pads are in widespread use, not merely to provide warmth, but also to afford a degree of relief or therapy for various conditions. In applying heat to the surface of the body, one may do so by convection, by direct contact with a warmed substance; that is, by conduction, or by radiating energy into the body.
Difficulty has heretofore been experienced in effectively applying heat which is electrically or otherwise generated to a patient. When transferring heat inwardly through living tissue to a problem region underlying the skin, if the heat applied to the skin surface is within a tolerable temperature range, then not enough heat energy is transferred to this site to afford beneficial effects.
As pointed out in chapter 10, "Therapeutic Heat" in the text Therapeutic Heat and Cold, edited by Justuf F. Lehmann and published in 1982 by Williams and Wilkins, it is generally accepted that heat produces desirable therapeutic effects, for it increases the extensibility of collagen tissues, it decreases joint stiffness, and it affords pain relief. Moreover, heat relieves muscular spasms, it aids in the resolution of inflammatory infiltrates, edema and exudates, and it enhances blood flow.
As indicated in the Lehmann text, superficial heat is commonly tied in with various forms of heating media such as a paraffin bath, hot air or hot water and radiant heat (infrared). For a given patient, the temperature sensitivity threshold is that temperature level of the heating medium to which the patient is exposed, above which the patient experiences undue discomfort. Thus temperature levels of the medium below the sensitivity threshold are more or less tolerable, whereas those above the threshold are effectively intolerable. If, for example, a patient being subjected to thermotherapy finds that the heat is more than he can stand and wishes the procedure discontinued, clearly the heat of the medium to which he is exposed is above his sensitivity threshold.
One must bear in mind that the temperature sensitivity threshold is determined on the basis of continuous exposure to the heating medium, for one can tolerate much higher heat levels when one is only exposed momentarily or intermittently to high temperatures.
The temperature sensitivy threshold depends on the nature of the heating medium. Thus, as noted in the Lehmann text, when the medium is hot water which is at the same temperature and is applied to the patient in the same fashion as heated paraffin which has a low heat capacity, the paraffin can be tolerated by a patient but the hot water is intolerable for it has a high specific heat and a high order of thermal conductivity.
As a consequence, with conventional heating techniques, regardless of the medium used, when the patient is continuously exposed to a heating medium which is at a substantially constant temperature level, though this level is high enough to bring about adequate heat transfer to the problem region underlying the exposed skin, then the skin temperature is usually well above the tolerable level and this may result in extreme discomfort to the patient and even to the burning of tissue.
It is also now recognized that by heating tumors to a higher temperature than the surrounding tissue, the tumor may be caused to shrink and disappear. As noted in The New York Times of Apr. 14, 1982 (section C2) in an article on modern approaches to cancer treatment, the effectiveness of heat therapy is based on the fact that cancers have poor circulation and a reduced ability to dissipate heat. "Thus a temperature of more than 113 degrees Fahrenheit could destroy cancer cells while sparing normal tissue."
In order to generally demonstrate the value of thermotherapy in the treatment of problem regions, we shall consider the backache, one of the most common of all human afflictions. As noted in the "Book of Back Care," published by the American Medical Association, most of us at some time in our lives suffer from backache.
The back, an extraordinarily complex structure, is composed of bones, cartilage, nerves, blood vessels, and layers upon layers of muscle, each with its own potential for causing trouble. In physical therapy, heat is most often used to help relax tense and spastic back muscles. As indicated in the "Book of Back Care," heat is usually applied to the skin overlying the problem region with hot towels, hot water bottles, electric heating pads, infrared lamps or paraffin baths.
Because in all conventional heat applicators, the heat is applied continuously to the skin area overlying the problem region, this imposes strict limits on the acceptable temperature level. Thus if one seeks to have the heat penetrate more deeply into the body, the temperature at the surface area must be raised to promote more rapid heat transfer, for the higher the differential between the internal and external temperatures, the greater the rate of transfer. But a point is then quickly reached at which the patient is made uncomfortable--for one can only tolerate continuously applied heat whose temperature level is not excessively above body temperature. The temperature sensitivity threshold for a given patient is that temperature level of the heating medium to which the patient is continuously exposed above which the patient experiences serious discomfort.
Because continuous heat therapy techniques, to be completely safe, must operate at a relatively low temperature level not much higher than the sensitivity threshold, they are of limited effectiveness in the treatment of backache and other painful conditions that are relieved by heat. And in the case of tumors, the practical problem encountered when applying heat thereto continuously is that the temperature necessary to raise the tumor temperature to a level destroying cancer cells cannot be tolerated at the skin surface overlying the tumor.
The concern of the present invention is not with the heat treatment of any particular medical condition or problem region, but with a more effective thermotherapy applicator therefor.
The prior Guibert U.S. Pat. No. 4,667,658 discloses a technique for applying therapeutic heat to a skin surface area of a patient whose threshold of sensitivity is determined by that temperature level of the heating medium to which the patient is continuously exposed, above which the patient experiences discomfort or injury. In this technique, the skin surface is exposed to a heating medium whose temperature is at a base level that is well above ambient but no higher than the temperature sensitivity threshold, the temperature of the medium being periodically raised above the base level to create high heat energy pulses whose peak temperatures are much higher than the threshold.
The duty cycle of these pulses is such as to allow for internal heat transfer to take place in the region below the exposed area of the patient in the intervals between pulses to an extent preventing an excessive rise in temperature at the skin surface whereby the patient gains the benefit of high heat energy treatment without discomfort or injury.
To carry out this technique, the Guibert patent discloses an instrument in which a motor-driven centrifugal air blower operated at a constant speed draws air from the atmosphere at ambient temperature and blows this air through an applicator which can be oriented to direct the hot air stream to impinge on the localized skin surface of the patient being treated, the hot air then being discharged into the atmosphere.
Mounted at the inlet of the blower motor is an electrical heater coil which acts to heat the air drawn into the blower. An electronic controller is interposed between the heater element and a high voltage supply to energize the heater with a relatively low voltage to establish the base temperature level in the pulsatory heating pattern to which the patient is subjected. The electronic controller is periodically bypassed by means of a repeat cycle timer, whereby the high voltage from the supply is then directly applied to the heater element to raise the air temperature of well above the base level to create high energy pulses whose peaks are much higher than the threshold.
In this Guibert instrument, the blower and the heater are mounted in a casing having an outlet coupled by a flow tube terminating in a universal joint on which the applicator is supported. This necessitates a stand to support the instrument, and it is not possible with this arrangement to bring the applicator to the patient and to apply the applicator to any desired skin surface area regardless of its location, for the patient must be brought to where the instrument is installed, and there are distinct limits as to where the applicator may then be applied. If, for example, it is necessary to apply thermotherapy to the legs of a horse, as a practical matter, it is impossible to do this with the instrument disclosed in the prior Guibert patent.
And while an instrument of the type disclosed in the prior Guibert patent is suitable for professional use in a physician's office or in a hospital, because of its cost, size and complexity, it does not lend itself to domestic use in the home of a patient or in the field where portability is a factor.
Also, a practical drawback of the instrument disclosed in the prior Guibert patent arises from the fact that the heated air produced by the instrument is discharged from the patient's skin into the atmosphere. Since each heater used with this instrument consumes well over 750 watts, the temperature of the air in the room or office in which the instrument is installed rises to a distinctly uncomfortable level, particularly if the instrument is being used repeatedly in the course of a day to treat patients.
Moreover, since the elevated air temperature in the room or office is being continuously drawn into the blower of the instrument and is no longer at ambient temperature, this makes it difficult to maintain constant the desired temperature levels of the thermotherapy heat pattern.
It must be borne in mind that to carry out the pulsatory thermotherapy technique effectively, it is important that the surface temperature of the skin be maintained at a base level which is below the sensitivity threshold, and if the base level temperature continues to rise, the instrument will not be effective.
The reason the instrument discloses in the prior Guibert patent requires high-wattage electric heaters is that all air fed into the heaters is at ambient temperature and at a constant air flow volume. In order to attain a desired peak temperature level which is much higher than ambient, one must provide high-wattage heaters. Such heaters and the power consumed thereby add substantially to the construction and operating costs of the instrument.
Also of prior art interest are the Guibert U.S. Pat. Nos. 4,398,535; 4,461,299 and 4,595,008.